Work-hardenable refractory carbide tool steels



Jan. 27, 1970 A. PRILL ETAL 3,

WORK-HARDENABLE REFRACTORY CARBIDE TOOL STEELS Filed ma 10, 1967 FIGS INVENTORS ARNOLD L. PRILL JOHN S. DICKSON ATTORNEY United States Patent Office 3,492,101 Patented Jan. 27, 1970 3,492,101 WORK-HARDENABLE REFRACTORY CARBIDE TOOL STEELS Arnold L. Prill and John S. Dickson, Suffern, N.Y., as-

signors to Chromalloy American Corporation, West Nyack, N.Y., a corporation of New York Filed May 10, 1967, Ser. No. 637,402 Int. Cl. B21d 33/00 US. Cl. 29--182.7 17 Claims ABSTRACT OF THE DISCLOSURE A work-hardenable refractory carbide tool steel composition is provided for use as carbide inserts in percussion tools, for example in rock bits and the like, the composition comprising about to 85% by volume of refractory carbide particles dispersed through a steel matrix. The steel matrix contains by weight about 0.8% to 1.5% carbon, about 10% to manganese, and the balance essentially iron. Advantageously, the composition may contain 35% to 85% by volume of refractory carbide. Examples of refractory carbide are those selected from the group consisting of titanium carbide, columbium carbide, tantalum carbide, vanadium carbide, solid solutions of these carbides, and solid solutions of titanium carbide with tungsten carbide.

This invention relates to a work-hardenable refractory carbide tool steel and, in particular, to work-hardenable carbide inserts for percussion tools and the like.

Refractory carbide tool steels are known containing particles of titanium carbide dispersed through a heattreatable steel matrix. Such a tool steel is disclosed in US. Patent, No. 2,828,202. The steels are advantageously produced by using powder metallurgy techniques. Finely divided particles of refractory carbide, such as titanium carbide, are uniformly mixed with powdered steel-forming ingredients and the mixture then compacted into a desired shape. The compact is heated to an elevated temperature under non-oxidizing conditions, e.g. in a vacuum, the temperature preferably being above the melting point of the steel-forming ingredients and below the melting point of the carbide. Generally speaking, the temperature does not exceed about 100 C. above the melting point of the steel matrix. The foregoing method is referred to in the art as liquid phase sintering.

As a result of the sintering, the compact densifies and, upon cooling, the metallographic structure comprises a substantially uniform dispersion of carbide particles through a steel matrix. While the composition produced will be hardened to a certain extent because of the presence of substantially large amounts of carbides, it can be further hardened by quenching it from an austenitizing temperature to room temperature to form a martensitic steel matrix. A hardness of up to about 72 R is obtainable by this heat treatment.

The refractory carbide, which may be present in amounts ranging from about 15% to 85 by volume of the total composition, confers wear resistance to the sintered product.

This property is highly desirable in certain types of tools, such as percussion tools. In rock bits, for example, the hard insert is subjected to severe vibrational and impact forces which the insert must withstand without shattering or breaking. Titanium carbide tool steels of the type described hereinabove are not very useful as inserts for rock bits in their fully hardened condition. The insert tends to break when subjected to high impact forces. One method tried for over-coming this problem comprised tempering the steel matrix to a lower hardness of about, for example 60 R in order to toughen it. While this was helpful insofar as minimizing brittleness was concerned, it was generally accompanied by a decrease in wear resistance.

Titanium car-bide is much harder than the surrounding steel matrix when the steel matrix is tempered. Because of the difference in hardness between the two phases, selective wearing away of the matrix tends to occur under aggravated conditions, particularly when the carbide insert is employed in percussion tools. When such type of wearing occurs, the carbide particles tend to dislodge from the matrix until finally the working portion of the insert wears away.

Attempts to overcome the foregoing problem have been in the direction of surface hardening the steel matrix between the hard particles by using a process referred to as nitriding so as to minimize the difference in hardness between the two phases with the aim of inhibiting selective wearing of the matrix and thus prevent dislodgement or falling out of the hard carbide particles. The advantage of this is that a hard surface is provided in conjunction with a tough core. While this has helped to some extent, the nitrided surface would gradually wear away and expose the softer base metal, whereby the matrix metal would be subjected to further selective wearing followed by dislodgement or falling out of the hard carbide particles.

It would be desirable to provide a refractory carbide tool steel wherein the matrix surrounding the hard carbide particles is tough but is capable of being surface hardened during use and thus minimize the problem of selective wearing.

It is thus the object of the invention to provide a novel refractory carbide tool steel composition characterized in that carbide particles are substantially uniformly dispersed through a steel matrix and characterized further in that the steel matrix is capable of being hardened by working.

Another object is to provide a work-hardenable refractory carbide insert for percussion tools, e.g. rock bits, eX- hibiting improved resistance to wear.

A further object is to provide a percussion tool having inserts of a refractory carbide tool steel characterized by improved resistance to wear.

A still further object is to provide a rock bit having carbide inserts capable of being work hardened during use.

These and other objects will more clearly appear when considered with the following discosure and the accompanying drawing, wherein:

FIGS. 1 and 2 are illustrative of one embodiment of a percussion tool, e.g. a rock bit, with which the carbide insert of the invention may be employed;

FIG. 3 depicts one form of carbide insert for use in rock bits;

FIGS. 4 and 5 are illustrative of another embodiment of a percussion tool; and.

FIG. 6 shows an insert for use with the tool of FIGS. 4 and 5.

Stating it broadly, the work-hardenable refractory carbide tool steel provided by the invention comprises about 15 to by volume of refractory carbide particles dispersed through a steel matrix making up substantially the balance, the steel matrix containing by weight about 0.8% to 1.5% carbon, about 10 to 20% manganese and the balance essentially iron. By the balance essentially iron is meant that the steel may contain other ingredients in amounts which do not adversely affect the work-hardening characteristics of the manganese steels. Such additional ingredients may include up to about 3% silicon, up to about 3% or 5% nickel and, if desirable, small amounts of cobalt, vanadium, chromium, molybdenum, nitrogen, etc., may be present.

Advantageously, the steel matrix may contain about to by weight of manganese. A steel composition particularly advantageous as a matrix is one containing by weight approximately 1.1% to 1.3% carbon, approximately 12% to 14% manganese and the balance essentially iron.

Examples of refractory carbides which may be employed in producing the wear resistant refractory carbide tool steels include titanium carbide, columbium carbide, tantalum carbide, vanadium carbide, mixtures or solid solutions of these carbides with each other, and solid solutions of titanium carbide with tungsten carbide. An example of a solid solution of titanium carbide-tungsten carbide is one in which the titanium carbide is saturated with tungsten carbide. Advantageously, such carbides may be present in the composition in amounts ranging from about to 85% by volume and, more advantaegously, in amounts ranging from about 65% to 85% by volume. These compositions are particularly advantageous as working elements for percussion tools.

The term percussion too is used herein in the broad sense. Such tools include cable drilling bits, rock bits, hammer mills, the working elements of jaw crushers and grinding mills, and the like. Generally speaking, such tools are characterized by a body portion to which is attached a carbide insert or element, the insert or element being the working portion of the tool.

By controlling the composition of the steel matrix over the ranges stated hereinbefore, particularly over the range of about 10% to 15% manganese, about 1% to 1.5% carbon, and the balance essentially iron, a carbide tool steel is provided having a high work-hardening propensity during use. For example, in the case of rock bits work-hardening is usually induced by impact or light blows, even if they are of high velocity, as prevail in rock drilling. Such types of working, while they cause only shallow deformation with a thin hardened skin, surface hardening may be high. Such surface hardening combines with the carbide particles to provide the desired wear resistance and also helps to maintain and anchor the hard carbide particles in place. The steel matrix is basically austenitic until it is work hardened, whereby the surface of the matrix is converted to hard martensite. Thus, the steel matrix has a tough interior of austenite but a very hard exterior. The work hardening capacity at the surface is very high and can be raised from a hardness of 170 to 200 Brinell to as high as 600 or higher. This type of hard surface, unlike a nitrided surface, is unique in that it renews itself during use. Thus, the carbide particles are maintained suitably anchored in the matrix, since the steel matrix surrounding the particles does not selectively wear away as much as other steels and since the surface-hardened steel matrix is continuously maintained throughout its use.

Examples of compositions provided by the invention are as follows:

EXAMPLE 1 About 25% by volume titanium carbide, about 75% by volume of a manganese steel containing by weight: about 11% manganese, about 1.2% carbon, and the balance essentially iron.

EXAMPLE 2 About by volume columbium carbide, about by volume of a manganese steel containing by weight: about 13% manganese, about 1.1% carbon, and the balance essentially iron.

EXAMPLE 3 About 50% by volume titanium carbide, about 50% by volume of a manganese steel containing by weight: about 14% manganese, about 1.4% carbon, and the balance essentially iron.

4 EXAMPLE 4 About 55% by volume of tantalum carbide, about 45% by volume of a manganese containing by weight: about 16% manganese, about 2% chromium, about 1.1% carbon, and the balance essentially iron.

EXAMPLE 5 About 65 by volume of titanium carbide, about 35% by volume of a manganese steel containing by weight: about 12% manganese, about 3% nickle, about 1.2% carbon, and the balance essentially iron.

EXAMPLE 6 About by volume of a saturated solid solution of titanium carbide-tungsten carbide, about 15% by volume of a manganese steel containing by weight: about 10% manganese, about 1.4% carbon, and the balance essentially iron.

An example of a rock bit using the carbide insert provided by the invention is shown in FIGS. 1 and 2, FIG. 1 being a plan view of the rock bit shown in elevation in FIG. 2. FIG. 3 is representative of one form of insert which may be employed in the rock bit.

Referring to FIGS 1 and 2, the rock bit is shown as comprising a body portion 1 having four radial wings 2 and a centrally located discharge opening 3 for air. Each wing is provided with a slot 3 in which is brazed a carbide insert 4. A similar insert is shown in perspective in FIG. 3. The end 5 of the body has a threaded opening 6 for receiving a drill stem in threading engagement therewith.

FIGS. 4 and 5 is another embodiment of a percussion tool comprising a body portion 10 having a working head 11 divided into three radially disposed portions or wings 12, 13 and 14. Each of the radial portions is provided recesses 15 for receiving carbide inserts of the type shown in FIG. 6. This type of insert need not be brazed into the recesses but may be interference pressfitted into the recesses. The insert 16 has a spherical top 17 and a slightly bevelled butt end 18 to aid in its interference insertion into the recess. As will be noted from FIGS. 4 and 5, the head of the bit is provided with peripheral notches 19 and channels 20 to enable withdrawal of rock particles during drilling, the center of the head and the channels being provided with discharge holes 21 for discharging water or air.

In producing the insert, the method employed comprises mixing the ingredients together, forming the mixture into a shape of an insert and sintering the shape at an elevated temperature for a time sutficient to obtain substantially full densification. Broadly, this method comprises mixing the appropriate amount of steel-forming ingredients with the appropriate amount of the primary carbide, using a small amount of wax to give sufiicient green strength to the resulting pressed compact, for example one gram of wax for each grams of mixture. The mixture may be shaped a variety of ways. We prefer to press the mixture to a density at least 50% of true density by pressing over the range of about 10 t.s.i. to 75 t.s.i, preferably 15 t.s.i. to 50 t.s.i,, followed by sintering under inert conditions, eg in an inert atmosphere or in a vacuum. The temperature employed is above the melting point of the steel matrix, for example at a temperature up to about 100 C above the melting point for a time sufficient for the primary carbide and the matrix to reach equilibrium and to obtain substantially complete desification, for example for about one minute to six hours.

When the liquid phase sintering is completed, the product is alowed to furnace cool to room temperature. If necessary, the as-sintered product is subjected to mechanical cleaning. Heating for 1 to 6 hours from 475 C. to 700 C. renders the sintercd compact more easily machinable.

Toughening of the composition is achieved by heating the alloy to an austenitizing temperature, e.g. in the range of about 850 C. to 1250 C. for a time sufficient to convert substantially the matrix to a face centered cubic structure, e.g. one minute to three hours, more advantageously above 20 minutes. The steel is then subsequently quenched by cooling in oil or water, whereby to retain substantially all of the austenite. The heat treating temperature will vary with the car-bon content. For example, where the carbon content is on the high side of the range, the austenitizing temperature should be at the upper portion of the range disclosed hereinabove.

After the compact has been austenitized, it may be subjected to a cleainng operation, for example by vapor blasting. Where the compact is afinished insert for a particular rock bit, it may be shot peened in order to produce a highly cold worked surface having a high hardness. An insert or other carbide element treated in this manner will have a microstructure characterized by a substrate or tough core of austenite and a very hard surface of martensite. As stated, hereinbefore, the surface renews itself under working conditions and thus a hard surface is always assured.

That the carbide steel of the invention has a high propensity for work hardening is apparent from a test conducted with a compact produced by sintering together a pressed powder mixture containing 45 volume percent titanium carbide and the balance manganese steel containing by weight 12 to 14% manganese, 1 to 1.2% carbon and the balance essentially iron. After austenitizing the carbide steel, the compact was subjected to high speed cutting by a saw. The carbide steel worked hardened so much it could not be cut.

The primary carbides of the group, TiC, VC, CbC and TaC may include limited amounts by Weight of other carbides, such as mixtures with up to about 50% molybdenum carbide, up to about chromium carbide, up to about 25% zirconium carbide, and the like. The total amounts of other carbides will generally range up to about 50% by weight of the primary carbides present.

The invention also provides a work-hardenable heat treatable refractory carbide tool steel for use in blanking dies, forming dies, drawing dies, drills and the like.

What is claimed is:

1. A work-hardenable sintered refractory carbide tool steel alloy comprising about to 85 volume percent of refractory carbide particles dispersed through an austenitic steel matrix making up substantially the balance, said steel matrix containing by weight about 0.8% to 1.5% carbon, about 10 to manganese and the balance essentially iron.

2. The steel of claim 1 wherein the refractory carbide is selected from the group consisting of titanium carbide, columbium carbide, vanadium carbide, tantalum carbide, mixtures with each other, and solid solutions of titanium carbide-tungsten carbide.

3. The carbide steel of claim 2 wherein the refractory carbide is titanium car-bide.

4. The carbide steel of claim 3 wherein the titanium carbide ranges from about to 85% by volume of the composition and wherein the steel matrix contains about 10% to 15% by weight of manganese.

5. The carbide steel of claim 2 wherein the refractory carbide is a solid solution of titanium carbide-tungsten carbide.

6. The carbide steel of claim 5 wherein the refractory carbide ranges from about 35% to 85 by volume of the composition.

7. The carbide tool steel of claim 4 wherein the steel matrix contains by weight approximately 1.1% to 1.3% carbon, approximately 12 to 14% manganese and the balance essentially iron.

8. A percussion tool comprising a metal body having at least one refractory carbide insert formed of the alloy in accordance with claim 1.

9. The percussion tool of claim 8 wherein the refractory carbide in the insert is selected from the group consisting of titanium carbide, columbium carbide, vanadium carbide, tantalum carbide, mixtures of these carbides with each other, and solid solutions of titanium carbide-tungsten carbide.

10. The percussion tool of claim 8, wherein the surface of the carbide insert is in the work hardened condition and is comprised of martensite, and wherein the substrate is austenite.

11. The percussion tool of claim 9 wherein the refractory carbide of the insert ranges in composition from about 65% to 85% by volume and wherein the steel matrix contains about 10% to 15% by weight of manganese.

12. The percussion tool of claim 11 wherein the steel matrix of the carbide insert contains by weight approximately 1.1% to 1.3% carbon, approximately 12 to 14% manganese and the balance essentially iron.

13. A work-hardenable sintered carbide tool insert formed of the alloy in accordance with claim 1.

14. The carbide tool insert of claim 13, wherein the surface of said insert is in the work hardened condition and comprises martensite and wherein the substrate is austenite.

15. The carbide insert of claim 13, wherein the refractory carbide is selected from the group consisting of titanium carbide, columbium carbide, tantalium carbide, vanadium carbide, and mixtures of these carbides with each other, and solid solution of titanium carbide-tungsten carbide, wherein the amount of carbide ranges from about 65 to 85% by volume, and wherein the steel matrix contains about 10% to 15% by weight of manganese.

16. The carbide insert of claim 15 wherein the refractory carbide is titanium carbide.

17. The carbide insert of claim 16 wherein the steel matrix contains approximately 1.2% carbon, approximately 12% to 14% manganese and the balance essentially iron.

References Cited UNITED STATES PATENTS 3,053,706 9/1962 Gregory 148--131 3,183,127 5/1965 Gregory l48131 3,369,891 2/1968 Tarkan 148131X 3,369,892 2/1968 Ellis 148-31X 3,380,861 4/1968 Frehn 148-31 3,450,511 6/1969 Frehn 29182.8

CARL D. QUARFORTH, Primary Examiner ARTHUR J. STEINER,,.Assistant Examiner U.S. Cl. X.R. 

